Packaging device and method of making the same

ABSTRACT

The present disclosure relates to an integrated chip packaging device. In some embodiments, the packaging device has a first package component. A metal trace is arranged on a surface of the first package component. The metal trace has an undercut. A molding material fills the undercut of the metal trace and has a sloped outermost sidewall with a height that monotonically decreases from a position below a top surface of the metal trace to the surface of the first package component. A solder region is arranged over the metal trace.

REFERENCE TO RELATED APPLICATION

This Application is a Continuation of U.S. application Ser. No.13/434,256 filed on Mar. 29, 2012, the contents of which is herebyincorporated by reference in its entirety.

BACKGROUND

Bump-on-Trace (BOT) structures were used in flip chip packages, whereinmetal bumps are bonded onto metal traces in package substrates directly,rather than bonded onto metal pads that have greater widths than therespective connecting metal traces. The BOT structures, compared withbonding structures bound to metal pads, help to reduce chip areas, andlower the manufacturing cost of the integrated circuit (IC) having BOTstructures. In some applications, the BOT structures may achieve thesame reliability as the conventional bond structures that are based onmetal pads.

During the BOT manufacturing process, the metal bumps are soldered ontorespective metal traces on the substrate by a reflow process. Areflowing process is a process in which solder is attached to a firstconductive member, melted by heat, and then solidified. In someapplications, the melted solder is caused to be in contact with both thefirst conductive member and a second conductive member, and then thesolder connects the first and second conductive members after beingsolidified. Heating may be accomplished by passing the structure througha reflow oven or under a heating device, or by soldering individualjoints with a hot air pencil.

During the reflowing process, the resulting packaging component needs tobe cooled down from the hot reflow condition to room temperature. Thedrop in temperature would cause the metal traces and the substrate tocontract. Because the metal traces and the substrate have differentcoefficient of thermal expansions (CTEs), the mismatch in the respectiveCTEs creates stress at the interface between the metal traces and thesubstrate. The CTE mismatch and the stress caused by the mismatch wouldresult in the trace being dislocated from the substrate, which is alsoreferred to as a phenomenon called “peeling.” This dislocation of themetal traces from the substrate, i.e., peeling, would cause thepackaging device to fail prematurely.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a first package component inaccordance with one or more embodiments;

FIGS. 2A and 2B are cross-sectional views of a second package componentin accordance with one or more embodiments;

FIGS. 3 and 4 are cross sectional views of the second package componentat different processing stages in accordance with one embodiment of thepresent disclosure; and

FIGS. 5A and 5B are cross-sectional views of a package comprising thefirst and the second package components.

DETAILED DESCRIPTION

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

Packages comprising Bump-on-Trace (BOT) structures are provided inaccordance with embodiments. The variations of the embodiments arediscussed. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements.

FIG. 1 is a cross-sectional view of package component 100 in accordancewith one or more embodiments. In some embodiments, package component 100is a device die that includes active devices 103 (such as transistors)therein. In some alternative embodiments, package component 100 is apassive component that does not have active devices therein. In anembodiment wherein package component 100 is a device die, substrate 102may be a semiconductor substrate such as a silicon substrate, althoughit may include other semiconductor materials. Interconnect structure104, which includes metal lines and vias 106 formed therein andconnected to active devices 103, is formed over substrate 102. In someembodiments, metal lines and vias 106 comprise a material includingcopper or copper alloys, and are formed using damascene processes.Interconnect structure 104 may include an Inter-Layer Dielectric (ILD)and Inter-Metal Dielectrics (IMDs) 108. IMDs 108 may comprise lowdielectric constant (low-k) dielectric materials, and may havedielectric constants (k values) lower than about 3.0. The low-kdielectric materials may also be extreme low-k dielectric materialshaving k values lower than about 2.5, for example. Package component 100may further include metal pad 109, Under-Bump Metallurgy (UBM) 110 onmetal pad 109, and metal pillar 112 on UBM 110. Metal pillar 112 maycomprise a copper pillar, and hence is referred to as copper pillar 112,copper-containing bump 112, or metal bump 112 hereinafter. Metal pillar112 may further comprise a nickel layer, a palladium layer, a goldlayer, or multilayers thereof, which layer(s) are collectivelyidentified by reference numeral 114. In at least one embodiment, soldercap 130 may be formed on copper pillar 112, for example, by plating asolder layer on the top of copper pillar 112, and then reflowing thesolder layer.

FIG. 2A is a cross-sectional view of another package component 200.Package component 200 may be a package substrate, although it may beanother type of package component such as an interposer, for example.Package component 200 may include metal lines and vias 202interconnecting the metal features that are on opposite sides of packagecomponent 200. In at least one embodiment, metal trace 210 is located ata top surface of package component 200, and may be electricallyconnected to connectors 212 on the bottom side of package components 200through metal lines and vias 202. Connectors 212 may be solder balls,metal pillars with solder caps thereon, metal pads, or the like. Metallines and vias 202 may be formed in dielectric layers 214, which may belaminate films, for example. In some alternative embodiments, metallines and vias 202 may be formed in a semiconductor substrate (such as asilicon substrate, not shown) or a dielectric core (not shown), and alsoin the dielectric layers that are formed on the semiconductor substrateor the dielectric core. In some embodiments, metal trace 210 comprises amaterial including copper, aluminum copper, tungsten, nickel, palladium,gold, and/or combinations thereof.

FIG. 2B is a cross-sectional view of the package structure 200 shown inFIG. 2A, wherein the cross-sectional view is obtained from the planecrossing line 2A-2A′ in FIG. 2A. As shown in FIG. 2B, when metal traces210 were formed on the substrate 214, undercuts 211 appear on the twoedges along the length of the metal traces 210 at the interface betweenthe metal traces 210 and the substrate 214. During the heating and thesubsequent cooling in conjunction with performing a reflow process, thestress caused by thermal contraction and expansion and CTE mismatch asdiscussed above would cause the undercuts 211 to develop into cracks.These cracks would propagate toward the centerlines 220 of the metaltraces 210 and thereby eventually “peel” the metal traces 210 away fromthe substrate.

FIG. 3 is a cross sectional view of the second package component 200after a liquid molding process in accordance to this disclosure. In someembodiments, before the packaging components 100 and 200 are beingassembled into one integrated piece of packaging device, a liquidmolding process is applied to the packaging component 200. The liquidmolding process comprises injecting a liquid molding material 230, suchas a curable liquid, over the package component 200, so that the curableliquid 230 fills the undercuts 211 on the sides of the metal traces 210.In this embodiment, as FIG. 3 shows, the curable liquid 230 covers theentirety of metal traces 210. The liquid molding process can be carriedout by any applicable means using applicable liquid molding apparatus.In some embodiments, the curable liquid 230 is formed by using theprocess and apparatus described in U.S. Pat. No. 4,294,782.

FIG. 4 is a cross sectional view of the second package component 200after a plasma treatment in accordance to this disclosure. Thereafter,the overmolded surface of the metal traces 210 is treated by plasma. Insome embodiments, the plasma treatment is performed according to aprocess similar to the one described in WO 2003/41130. Plasma treatmentdiscussed here can comprise exposing the package component 200 to agaseous state activated by a form of energy externally applied andincludes, but not limited to, corona discharge, dielectric barrierdischarge, flame, low pressure glow discharge, and atmospheric glowdischarge treatment. The gas used in this plasma treatment can be air,ammonia, argon, carbon dioxide, carbon monoxide, helium, hydrogen,crypton, neon, nitrogen, nitrous oxide, oxygen, ozone, water vapor,combinations thereof, and others. In some alternative embodiments, othermore reactive gases or vapors can be used, either in their normal stateof gases at the process application pressure or vaporized with asuitable device from otherwise liquid states, such ashexamethyldisiloxane, cyclopolydiethylsiloxane,cyclopolyhydrogenmethylsiloxanes,cyclopolyhydrogenmethyl-co-dimethylsiloxanes, reactive silanes, andcombinations thereof. As FIG. 4 shows, while the plasma removes theliquid molding material (as represented by the dotted region 232) abovethe top surfaces of the metal traces 210, a portion of the liquidmolding material 234 that fills the undercuts 211 remains.

In this embodiment, the package component 200 may be overmolded using acurable liquid organic composition, a curable liquid silicone-organiccopolymer composition, or a curable liquid silicone composition. Thetype of curable liquid composition selected depends on various factorsincluding the type of die attach adhesive used.

Examples of suitable curable liquid organic compositions include curableliquid epoxies, curable liquid cyanate esters, and combinations thereof.Examples of suitable curable liquid silicone-organic copolymercompositions include curable liquid compositions that cure to formpoly(diorganosiloxane/organic) block copolymers such aspoly(diorganosiloxane/amide) copolymers.

Suitable curable liquid silicone compositions include condensationreaction curable liquid silicone compositions; addition reaction curableliquid silicone composition; ultraviolet radiation initiated curableliquid silicone compositions; and/or free radical initiated curableliquid silicone compositions.

Addition reaction curable silicone compositions may be used to minimizeby-products formed when curing, as compared to the other types ofcurable liquid silicone compositions. The addition reaction curableliquid silicone compositions may comprise (a) an organopolysiloxanehaving an average of at least two alkenyl groups per molecule, (b) anorganohydrogenpolysiloxane having an average of at least two siliconatom-bonded hydrogen atoms per molecule, and (c) a hydrosilylationcatalyst. The addition reaction curable liquid silicone composition mayfurther comprise one or more optional ingredients selected from (d) afiller, (e) a treating agent for the filler, (f) a catalyst inhibitor,(g) a solvent, (he) an adhesion promoter, (i) a photosensitizer, (j) apigment, (k) a flexibilizer, and combinations thereof.

Suitable fillers for component (d) include reinforcing fillers such assilica (e.g., fumed silica, fused silica, and ground silica), titania,and combinations thereof. In some alternative embodiments, component (d)may be thermally conductive, electrically conductive, or both. In somealternative embodiments, component (d) may comprise a combination ofconductive and nonconductive fillers. Component (d) may comprise DRAMgrade filler or a mixture of DRAM grade filler and filler of a lesserpurity than DRAM grade filler. Component (k) may comprise a long chainalpha-olefin, e.g., an olefin with 14 or more carbon atoms.

The curable liquid may be a one-part composition or a multiple-partcomposition such as a two-part composition. When an addition reactioncurable liquid silicone composition is formulated as a one-partcomposition, a hydrosilylation catalyst inhibition may be included. Whenan addition reaction curable liquid silicone composition is formulatedas a multiple part composition, any silicone containing ingredients arestored separately from any hydrosilylation catalyst.

The curable liquid is formulated to have a viscosity that will minimizewire sweep under the liquid injection molding conditions. Withoutwishing to be bound by any theory, it is thought that viscosity that istoo high will contribute to wire sweep, however, viscosity that is toolow may allow the curable liquid to leak from the mold. For someaddition reaction curable liquid silicone compositions viscosity may be80 to 3,000 Poise.

The curable liquid may be cured at a predetermined temperature for apredetermined period of time to have a cure speed that will minimizewire sweep under the liquid injection molding conditions. A cure speedthat is too fast may contribute to wire sweep, however, cure speed thatis too slow may render the process inefficient. For some additionreaction curable liquid silicone compositions, the curing of the curableliquid is performed at 80 to 240.degree. C. for 30 to 120 seconds, oralternatively at 80 to 180.degree. C. for 30 to 60 seconds, oralternatively at 80 to 150.degree. C. for 30 to 60 seconds.

Referring to FIG. 5A, package components 100 and 200 are bonded witheach other through solder region 140 (alternatively referred to as asolder bump). Solder cap 130 in package component 100 (FIG. 3) may bereflowed to form an entirety or a portion of solder bump 140. Solderbump 140 may be formed of a lead-free solder, a eutectic solder, or thelike. Solder bump 140 is bonded to, and contacts, the top surface ofmetal trace 210, wherein the top surface faces package component 100.After the bonding of package components 100 and 200, an underfill (notshown) may be filled into the space between package components 100 and200. Accordingly, the underfill is also filled into the space betweenneighboring metal traces 210, and may contact metal trace 210. In somealternative embodiments, no underfill is dispensed, while the air fillsthe space between package components 100 and 200, and fills the spacebetween neighboring metal traces 210.

FIG. 5B is a cross-sectional view of the package structure shown in FIG.5A, wherein the cross-sectional view is obtained from the plane crossingline 5B-5B′ in FIG. 5A. As shown in FIG. 5B, solder bump 140 may contactthe opposite edges of metal trace 210. In some applications, the bondstructure comprising copper pillar 112, solder bump 140, and metal trace210 collectively are also referred to as a BOT structure. Note that inthis embodiment, the undercuts 211 on both sides of the metal traces 210have been filled with liquid molding material (as depicted in FIG. 4).

In some embodiments, by filling the undercuts 211 of the metal traces210 at the interface between the metal traces 210 and the substrate 214,the undercuts 211 are protected from stresses caused by CTE mismatching,and the creation of cracks initiating at the undercuts 211 is prevented.Accordingly, the chances for “peeling,” which is caused by propagationof cracks originating from the undercuts 211 at the edges of the metaltraces 210, may be reduced.

Therefore, the present disclosure relates to a bump on trace (BoT)technique that attaches a die by solder to a metal trace. The BoTtechnique reduces trace peeling by filling undercuts with a moldingmaterial that protects the undercuts from stresses caused by CTE(coefficient of thermal expansion) mismatches.

In some embodiments, the present disclosure relates to an integratedchip packaging device. The device comprises a first package component,and a metal trace arranged on a surface of the first package component.The metal trace comprises an undercut. A molding material fills theundercut of the metal trace and has a sloped outermost sidewall with aheight that monotonically decreases from a position below a top surfaceof the metal trace to the surface of the first package component. Asolder region is arranged over the metal trace.

In other embodiments, the present disclosure relates to an integratedchip packaging device. The device comprises a metal trace arranged overa first package component. The metal trace comprises an undercut. Amolding material is arranged within the undercut of the metal trace. Themolding material has an outermost sidewall with a slope thatmonotonically decreases as a distance from the first package componentdecreases. A solder region is arranged over the metal trace.

In yet other embodiments, the present disclosure relates to a method offorming an integrated chip packaging device. The method comprisesforming a metal trace on a surface of a first package component, whereinthe metal trace comprises an undercut. The method further comprisesforming a molding material over an entirety of the metal trace, andremoving a part of the molding material from a top surface of the metaltrace and from a part of sidewalls of the metal trace. The methodfurther comprises forming a solder region on the top surface of themetal trace.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. An integrated chip packaging device, comprising:a first package component; a metal trace arranged on a surface of thefirst package component, wherein the metal trace comprises an undercut;a molding material that fills the undercut of the metal trace and thathas a sloped outermost sidewall with a height that monotonicallydecreases from a position below a top surface of the metal trace to thesurface of the first package component; and a solder region arrangedover the metal trace.
 2. The device of claim 1, wherein a top surface ofthe molding material is arranged between a top surface of the metaltrace and the surface of the first package component.
 3. The device ofclaim 1, further comprising: a second metal trace arranged on thesurface of the first package component and comprising a second undercut,wherein the molding material fills the second undercut but does notcontinuously extend over the surface between the metal trace and thesecond metal trace.
 4. The device of claim 1, wherein the solder regionsurrounds a top surface of the metal trace and sidewalls of the metaltrace above the molding material.
 5. The device of claim 4, wherein thesolder region contacts the sidewalls of the metal trace above themolding material.
 6. The device of claim 4, further comprising: a metalpillar arranged between the solder region and a metal pad on a surfaceof a second package component, wherein the second package component isdisposed over the first package component and the solder region contactsthe metal pillar; and an under-bump metallurgy having a non-planartopology, which is arranged between the metal pillar and the metal pad.7. The device of claim 1, wherein the molding material comprises acurable organic composition comprising curable epoxies, curable cyanateesters, or combinations thereof.
 8. The device of claim 1, wherein thefirst package component comprises a bottom surface facing an oppositedirection as the surface, and wherein the metal trace is electricallyconnected to one or more connectors on the bottom surface of the firstpackage component through metal lines and vias arranged within the firstpackage component.
 9. The device of claim 1, wherein the metal trace hasa length extending in a first direction and a width extending in asecond direction substantially perpendicular to the first direction;wherein the width is smaller than the length; and wherein the undercutis located along the length of the metal trace at an interface betweenthe metal trace and the first package component.
 10. An integrated chippackaging device, comprising: a metal trace arranged over a firstpackage component, wherein the metal trace comprises an undercut; amolding material arranged within the undercut of the metal trace,wherein the molding material has an outermost sidewall with a slope thatmonotonically decreases as a distance from the first package componentdecreases; and a solder region arranged over the metal trace.
 11. Thedevice of claim 10, further comprising: a second package componentdisposed over the first package component, wherein the solder region isarranged over the metal trace between the first package component andthe second package component.
 12. The device of claim 10, wherein themolding material is arranged within the undercut at a location that isbetween the first package component and the metal trace.
 13. The deviceof claim 10, wherein a top surface of the molding material is below atop surface of the metal trace.
 14. The device of claim 10, furthercomprising: a second metal trace arranged over the first packagecomponent and comprising a second undercut, wherein the molding materialis arranged within the second undercut and does not continuously extendover the first package component between the metal trace and the secondmetal trace.
 15. The device of claim 10, wherein the solder regionsurrounds a top surface and sidewalls of the metal trace above themolding material.
 16. The device of claim 15, wherein the solder regioncontacts the sidewalls of the metal trace above the molding material.17. A method of forming an integrated chip packaging device, comprising:forming a metal trace on a surface of a first package component, whereinthe metal trace comprises an undercut; forming a molding material overan entirety of the metal trace; removing a part of the molding materialfrom a top surface of the metal trace and from a part of sidewalls ofthe metal trace; and forming a solder region on the top surface of themetal trace.
 18. The method of claim 17, wherein the molding materialhas a sloped outermost sidewall with a height that monotonicallydecreases from a position below a top surface of the metal trace to thefirst package component.
 19. The method of claim 17, wherein the moldingmaterial comprises a curable liquid that is cured at a temperature ofbetween approximately 80° C. and 240° C.
 20. The method of claim 17,wherein a top surface of the molding material is below a top surface ofthe metal trace.